Stretchable cable

ABSTRACT

An elongated, uncoiled stretchable and retractable cable is formed with the capability of stretching several times its relaxed length and returning to its relaxed length without being damaged by having inner and outer conductors helically wrapped with opposite lays or serves which may move relative to each other without becoming interlocked as in a braided construction. More specifically, the inner one of the conductors is helically wrapped in one direction about and along a central, elastomeric core and the outer conductor is helically wrapped along and circumferentially about the inner conductor but in an opposite direction. In a similar manner, an outer conductor shield for a coaxial cable may be formed of conductors oppositely laid and helically wrapped about an elastomeric layer separating the shield conductors from the interior conductors. Good resistance to ambient and environmental conditions as well as good stretchability and retractability are provided by using thermoplastic, elastomeric polyurethane as the material for the inner central core, the insulating layer and an outer protective sheath.

United States Patent [i9] alters et al.

I 1 STRETCHABLE CABLE [75] Inventors: Jack E. Walters; Robert B. Cole,

' both of Richmond, Ind.

[73] Assignee: Belden Corporation, Chicago, Ill. [22] Filed: July 10, 1970 [21] Appl. No.: 53,873

1,848 0/1858 Great Britain 174/69 OTHER PUBLICATIONS dAdolf, Urethane Rubbers Growing in Use, Rubber World, Vol. 144, No. 4, 7/61, pp. 67-71, (TK1870.544).

POLYURETHANE ELASTOMER [11] 3,823,253 [451 July 9, 1974 Primary Examiner -Darrell L. Clay Attorney, Agent, or FirmFitch, Even, Tabin & Luedeka 5 7] ABSTRACT An elongated, uncoiled stretchable and retractable cable is formed with the capability of stretching several times its relaxed length and returning to its relaxed length without being damaged by having inner and outer conductors helically wrapped with opposite lays or serves which may move relative to each other without becoming interlocked as in a braided construction. More specifically, the inner one of the conductors is helically wrapped in one direction about and along a central, elastomeric core and the outer conductor is helically wrapped along and circumferentially about the inner conductor but in an opposite direction. In a similar manner, an outer conductor shield for a coaxial cable may be formed of conductors 0ppositely laid and helically wrapped about an elastomeric layer separating the shield conductors from the interior conductors. Good resistance to ambient and environmental conditions as well as good stretchability and retractability are provided by using thermoplastic, elastomeric polyurethane as the material for the inner central core, the insulating layer and an outer protective sheath.

2 Claims, 1 Drawing Figure POLYURETHANE ELASTOMER 1 STRETCHABLE CABLE This invention relates to uncoiled, stretchable and retractable cables which when stretched from a relaxed condition may elongate to several times their relaxed length and which are capable of returning to the relaxed length and diameter with release of tension thereon without deleterious effects on the electrical and physical properties of the cable.

Stretchable and flexible cables are used in a number of various environments and applications where elongation and retraction to the original relaxed state without damage is a necessary requirement. Typical applications for such cables include retractable cords, instrument cable for atomic energy tests, power tools, microphones, mobile radio, and other electrical communication applications. Often it is desired that the cable stretch as much as, for example, 300 percent relative to its original, relaxed length and that the cable return to its relaxed original length without any substantial damage to the electrical and physical characteristics of the cable.

One form of uncoiled, stretchable cable is made with a central elastic core thread about which is braided metallic conductor strands and finally an outer protective insulating sheath is formed over the braided conductor strands. The stretchability of cables of this kind is limited by the braided conductors moving and becoming interlocked with one another after a predetermined amount of stretch; any further stretching may cause damage to or breakage of one of the interlocked conductors.

More recently, it has been suggested that stretchable cables be formed with the electrical conductor formed as a solid metallic conductor, a single helically wound wire, or a plurality of wires braided together as above described. The cable also includes an internal diameter building material" layer formed of twisted nylon threads braided in a manner in which the threads bunch up while in a relaxed state and which is provided in the cable for the purpose of aiding elongation of the cable during stretching. When tensioned, the diameter building material is stated to reduce in diameter to a greater extent than solid materials thereby providing an additional diameter reduction ratio and a greater ability to elongate.

According to another recent suggestion, the inner stretchable core has been eliminated and the inner central portion of the cable is formed with an inner conductor wire having formed with parallel helices or with cross woven wires. The outer conductor shield of this coaxial cable may be similarly formed with wire having parallel helices or with cross woven wires. Thus, both these recent suggestions include the use of braided conductors for the shield which results in the possibility of conductors interlocking and becoming damaged when the cable is stretched.

Known cables of the uncoiled stretchable kind use woven fabric or thermosetting plastics for the outer protective sheath, but these sheaths deteriorate with age at too fast a rate for some applications. Thus, there is a need for a cable having a highly stretchable and contractable sheath material which does not readily lose its effectiveness with aging and which also has good oil resistance, fuel resistance, tear resistance, abrasion resistance, ozone resistance and weather resistance.

Accordingly a general object of the invention is to provide as contrasted with the prior art cables of the foregoing kind, a new and improved stretchable, rctractable and uncoiled cable.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawing in which:

FIG. 1 is a perspective view, with parts broken away, of a portion of a cable constructed in accordance with the invention.

As shown in the drawings for purposes of illustration, the invention is embodied in an uncoiled stretchable cable 11 having a capability ofstretching longitudinally from its original relaxed length to an extent at least greater than double its own length and, in the illustrated and described cable to 300 percent greater than its relaxed length. The cable 11 also is capable of returning upon release of tension forces to its original relaxed length and diameter without any substantial change in its electrical or physical characteristics, it being realized that after considerable stretching and retracting operations that the cable may not return precisely to its original relaxed length.

In accordance with the invention, the extensibility of the cable 11 is improved by wrapping electrical conductors l3 and 15 with a non-braided generally helically wrap about a central extensible core 17 with the conductors l3 wrapped with a lay or serve of a first direction and the conductors l5 wrapped with an oppositely directed lay or serve. Because the inner andouter conductors l3 and 15 are not woven as in braided, prior art stretchable cables, the conductors l3 and 15 are free to shift relatively to each other without becoming interlocked, interlocked conductors may damage one another with additional stretching ofthe cable. The inner and outer conductors are wound in opposite directions which have'an effect of being crossed over without actually being interwoven as in the case of a braid. This method allows reduced inductance as compared to a conductor composed of a single serve (one direction only). This double serve also does not have the disadvantage of a braid whose strands are interlocked thereby interfering with extension and retraction. The illustrated cable 11 is of the coaxial kind and further includes a stretchable and contractable insulating layer 18 about the inner and outer conductors l3 and 15. Inner and outer shield conductors 1 9 and 21 are also wrapped generally helically with opposite lays on the insulating layer 18 to provide good extensibility for the shield conductors. An outer sheath 23 of flexible, stretchable and contractable elastomeric material protects and surrounds the shield conductors.

Also, in accordance with another aspect of the invention, the inner core 17, insulating layer 18, and outer sheath 23 are formed of elastomeric, thermoplastic materials preferably a plastic, such as an elastomeric form of polyurethane, to reduce the effects of aging found with thermosetting materials usually used for stretchable cables and to provide the high elongation and resilience desirable for highly stretchable cables. Such elastomeric, thermoplastic materials also provide, as contrasted to commonly used thermosetting cable materials, increased cut through resistance, oil resistance, fuel resistance, tear resistance. ozone resistance, abrasion resistance, and weather resistance. Such a cable 11 may be formed of relatively smalldiameter yet with 3 good flexibility, stretchability and resistance to damage.

Referring now in greater detail to the illustrated embodiment of the invention, the inner core 17 may be an elongated rod, circular and solid in cross section and may be formed of elastomeric polyurethane having high resiliency and stretchability. Good results with elongation of 300 percent or more have been obtained using thermoplastic polyurethane as the core material. It is to be understood that other materials and various sizes of an inner core may be used and that the preferred materials (and the dimensions given hereinafter) are by way of example only and not by way of limitation. For example, styrene-butadiene may be used as the elastomeric material for the sheath, core, and insulating layer.

The inner set of electrical conductors 13 are wrapped helically around the central core 17 and against an outer surface 25 of the core 17 and the inner conductors 13 extend longitudinally along the core with a given lay, which is a counterclockwise lay as viewed from the left, exposed end of the cable 11 in FIG. 1. In this illustrated cable, approximately 24 conductors 13 of a 36 AWG size are helically wrapped about the central core 17 which is 0.125 inches in diameter. The pitch distance for the helix of the inner conductors is about .15 inch. With stretching of the cable 11 to about 300 percent of its relaxed length, the outer diameter of the conductors 13 reduces substantially from its 0.135 inch relaxed diameter. The conductors 13 may be formed of solid wire or copper, aluminum or other material or they may be formed with multiple strands and they may be varied considerably in size depending on the ultimate use and requirements for the cable.

The preferred outer conductors 15 are identical in size and number to that of the inner conductors 13 but wrapped with the opposite hand helix, viz. clockwise as viewed from the left exposed end. in FIG. 1. The outer conductors 15 are helically wound around and along the outer surfaces of the inner conductors 13 and are free to shift therealong during extension or contraction as well as when bending the cable about a small radius turn or bend. The sliding of the outer conductors 15 relative to the inner conductors 13 provides a freedom not possible with braided conductors in which the conductors become interlocked upon being stretched to a given extent. Also, the non-interlocking of the inner and outer cables eliminates the problem of kinking of conductors which sometimes occurs if crossed over conductors fail to properly return during the relaxation of the tension on the cable. Also, as above explained, the conductors 13 and 15 do not present the conductor inductance as in unidirection single, spiral, served constructions. In the illustrated cable, the forty-eight conductors 13 and 15 cover the entire peripheral surface of the core 17 with conductors.

When the cable 11 is of the coaxial kind, as illustrated, the insulating layer 18 separates the conductors l3 and 15 from the shield conductors 19 and 21. In this instance, the insulation layer 18 is a continuous cylinder or tube laid or otherwise formed on the outer surface of the conductors 15. Preferably, the insulating layer 18 is also formed of a highly flexible, stretchable and retractable, thermoplastic, elastomeric material such as, for example, polyurethane. The illustrated insulating layer 18 is approximately 0.040 inch thick and has an outer diameter of about 0.225 inch. This is in LII 4 contrast to the illustrated outer sheath which has a wall thickness of 0.030 inches.

The inner shield conductors 19 are wrapped generally helically around and along the outer surface 27 of the insulating layer 18 and with a counterclockwise lay, as viewed in FIG. 1. In this instance, the inner set of conductors 19 are formed of 32 conductors of a 30 AWG size and are helically wrapped with a pitch distance of about 0.25 inch. The outer diameter din1ension for the shield conductors is about 0.250 inches. The outer shield conductors 2| are, in this instance, identical in size and kind and are helically wrapped in the same manner but with a clockwise lay as the inner shield conductors 19. The outer shield conductors 21 are wrapped on the outer surfaces of the inner shield conductors l9 and are free to move relative thereto with elongation and contraction of the cable. In the illustrated embodiment of the invention, the 64 shield conductors 19 and 21 cover the entire peripheral surface of the insulating layer 18.

The cable 11 is completed with the provision of the outer shield jacket orsheath 23 surrounding the helically wrapped outer shield conductors 21 to protect and insulate the interior component of the cable 11. The preferred elastomeric material for the outer sheath is a thermoplastic, elastomeric polyurethane which is preferably of the same material as that of the center rod 17 and the insulation layer 18. Such polyurethane has been found to have several times the physical properties of thermosetting compounds used heretofore particularly as to tensile elongation, hardness, oil resistance, fuel resistance, tear resistance, abrasion resistance, ozone resistance and weather resistance. The illustrated sheath 23 has a relaxed outer diameter of 0.310 inches. When elongated to about 300 percent of its relaxed length, the outer diameter of the sheath is reduced to 0.1 inch. Upon release ofthe tension forces. the sheath expands to approximately its original diameter and the cable returns to its original relaxed length. As the conductors l3 and 15 are wound in oppostie directions, forces tending to kink them during return from a stretched to a relaxed condition are more balanced than are forces encountered when conductors are wound in a single direction and are allowed to return from a stretched to a relaxed condition.

While the extensible core 17 is formed as a solid rod in the illustrated embodiment of the invention, the extensible core 17 may be made in the form of a hollow tube for cables in which it is desired to reduce the amount of force required to produce a given extension.

The cable 11 is particularly useful for applications where elongation without damage is a requirement such as for use in instrumentation cables for atomic energy tests for connection to and from appliances, power tools, microphones, mobile radio, etc. In applications which do not require high current capacities and where a more limp construction is desired, tinsel conductors formed of thin metallic strips approximately 0.001 inch thick and about 0.005 inch in width and wound around textile or other suitable cores may be used and substituted for the conductors l3, 15, 19 and 21 above described.

From the foregoing it will be seen that the present invention is particularly directed to an uncoiled stretchable and retractable cable which is capable of considerable elongation, e.g. 300 percent and which will return to its original length and diameter without deleterious effects on its physical and electricalcharacteristics. Good resiliency and good stretchability are obtained by forming a central core and outer sheath of an elastomeric such as a thermoplastic, elastomeric polyurethane and by helically wrapping inner and outer conductors with opposite lays. Additionally, the use of polyurethane for the outer cable sheath provides increased advantages as to resistance to ambient environmental conditions and to the effects of aging.

While a preferred embodiment has been shown and described, it will be understood that there is no intent to limit the invention by such disclosure but, rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is: i

1. An elongated, uncoiled stretchable and retractable coaxial cable capable of stretching at least three times its relaxed length and contracting to its relaxed length without substantial damage thereto comprising an inner, elongated, central, stretchable and contractable core of elastomeric polyurethane material, a plurality of elongated first electrical, flexible conductors generally helically wrapped around and along said core in a first direction, a plurality of elongated second electrical conductors generally helically wrapped along and disposed circumferentially outward of the outer surface of said first conductor throughout substantially the entire length thereof, said second electrical conductors being helically wrapped in a direction opposite tothe helical winding of said first conductors, an insulating layer of stretchable and contractable, elastomeric polyurethane material surrounding said first and second conductors, a plurality of first shield conductors generally helically wrapped in one direction around and along said insulating layer, a plurality ol'second shield conductors generally helically wrapped around and along said first shield conductors in a direction opposite to said one direction, and an outer sheath of stretchable and contractable elastomeric, polyurethane material surrounding the assembly of said core, insulating layer, and said conductors.

2. A coaxial cable in accordance with claim 1 in which said first conductors cover substantially the entire peripheral surface of said core and in which said first shield conductors cover substantially the entire peripheral surface of said insulating layer. 

1. An elongated, uncoiled stretchable and retractable coaxial cable capable of stretching at least three times its relaxed length and contracting to its relaxed length without substantial damage thereto comprising an inner, elongated, central, stretchable and contractable core of elastomeric polyurethane material, a plurality of elongated first electrical, flexible conductors generally helically wrapped around and along said core in a first direction, a plurality of elongated second electrical conductors generally helically wrapped along and disposed circumferentially outward of the outer surface of said first conductor throughout substantially the entire length thereof, said second electrical conductors being helically wrapped in a direction opposite to the helical winding of said first conductors, an insulating layer of stretchable and contractable, elastomeric polyurethane material surrounding said first and second conductors, a plurality of first shield conductors generally helically wrapped in one direction around and along said insulating layer, a plurality of second shield conductors generally helically wrapped around and along said first shield conductors in a direction opposite to said one direction, and an outer sheath of stretchable and contractable elastomeric, polyurethane material surrounding the assembly of said core, insulating layer, and said conductors.
 2. A coaxial cable in accordance with claim 1 in which said first conductors cover substantially the entire peripheral surface of said core and in which said first shield conductors cover substantially the entire peripheral surface of said insulating layer. 